Mocking `useRouter` from Next.js is crucial when testing React components with Jest. Use `jest.mock` to create a mock, return useful values & test the `push` method separately.

Testing Custom Hooks in React with Jest & Enzyme: Call hook inside functional component, mock dependencies with jest.mock, useSearchParams & useRouter mocks. Example code covers 4 scenarios for testing custom hook behavior.

Next 15 makes searchParams asynchronous for optimization. Use async/await or React's new use hook for synchronous access.